On Thu, 17 Sep 2026, John Dammeyer wrote:
I wonder if I'm having the same problem.
I have a MESA 7i92H on a PC. I boot, I home all axis. Maybe jog around a bit.
Then hit the ESTOP to remove power to the drives, turn off monitor and leave
the shop. The PC stays running. A day or two later I come back and everything
is fine.
Or...
I get this message as shown in the attached latency.txt file.
Unexpected realtime delay on task 0 with period 1000000
This Message will only display once per session.
Run the Latency Test and resolve before continuing.
This error may not show up for days and never really when I'm working with the
system either running G-code or doing something manually.
If you have a Intel Ethernet chip on your PC do you have irq coalescing
disabled?
Do you have isolcpus=N with N set to the last core in you grub file?
If so do you also have the Ethernet IRQ pinned to the last core?
Suggestions?
Thanks
John
-----Original Message-----
From: Nicklas SB Karlsson [mailto:[email protected]]
Sent: September 17, 2026 1:31 PM
To: [email protected]
Subject: Re: [Emc-users] Ethernet send packets jitter
Nailed it down to recv(...) function call. Measured with 1 ?s resolution this
call usually take around 1 ?s but
sometimes it take up several thousand micro seconds. Previously measured
these delays of several milliseconds
seems to happen with a periodicity of 16 to 17 milliseconds corresponding
to a frequency of around 60 Hz. Rule
out noise from power grid since this is 50 Hz in Sweden.
Have not had time to try what you suggest yet but have a lot more time
tommorow.
Anybody have any about cause of these extra delays on recv(...) ??
Rule blocking call since data i sent in an Ethercat ring from a single thread.
With no Ethernet frames sent it
should either block or receive.
Nicklas Karlsson
tor 2026-09-17 klockan 07:28 -0700 skrev Peter Wallace:
On Thu, 17 Sep 2026, andy pugh wrote:
On Wed, 16 Sept 2026 at 21:20, Nicklas SB Karlsson <[email protected]>
wrote:
Running Linuxcnc and send receive Ethernet jitter is small for most
packets but sometimes there is delay of well
above on millisecond, running for maybe a minute or so worst case is
between 6...7 milliseconds.
Maybe you need to disable IRQ coalescing? It's mentioned briefly in
the hm2_eth docs, but also might be relevant to EtherCAT.
https://linuxcnc.org/docs/stable/html/man/man9/hm2_eth.9.html
(It's at least a google-able phrase for further investigation)
At least for hm2_eth, basic Network latency improvement methods are:
On Intel (and some less common others like broadcom), disable IRQ
coalescing
On Realtek, install the DKMS driver (the stock Linux driver has multi-ms
random latencies)
On all, use isolcpus (or whatever the newer scheme is called) to isolate the
last CPU, and then pin the Ethernet IRQ to that CPU.
Use the latest kernel (I have a test system that always got random
timeouts,
say once a day, with 6.x kernels, this was totally fixed with a 7.X kernel
--
atp
"A motorcycle is a bicycle with a pandemonium attachment and is
designed for the especial use of mechanical geniuses, daredevils and
lunatics."
? George Fitch, Atlanta Constitution Newspaper, 1912
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Peter Wallace
Mesa Electronics
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Mesa Electronics
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